If you have serious health problems because of your weight — and lifestyle changes have not resulted in significant weight loss — prescription weight-loss drugs may be an option. You should know, though, that prescription weight-loss drugs don't replace the need to make healthy changes in your eating habits and activity level.

Prescription weight-loss drugs are generally reserved for people who haven't been able to lose weight through diet and exercise, and who have health problems because of their weight. They're not for people who want to lose just a few pounds for cosmetic reasons.

Your doctor may consider weight-loss drugs for you if haven't been able to lose weight through diet and exercise and you meet one of the following:

Your body mass index (BMI) is greater than 30

Your BMI is greater than 27 and you have a serious medical problem related to obesity, such as diabetes or high blood pressure

Before selecting a medication for you, your doctor will consider your health history, possible side effects and potential interaction of weight-loss drugs with other medications you're taking.

When combined with a low-calorie diet and regular exercise, weight-loss drugs produce an average weight loss of 5 to 10 percent of total body weight within a year, which is a typical weight-loss goal. Diet and exercise are responsible for part of this weight loss, and medications are responsible for part as well.

Losing 5 to 10 percent of your total weight may not seem like much, but even modest weight loss can improve your health by:

Decreasing blood pressure

Decreasing lipid levels

Decreasing blood glucose levels

Increasing insulin sensitivity

It's important to keep in mind, however, that these medications may not work for everyone. And when you stop taking these medications, you're likely to regain much or all of the weight you lost.

Diethylpropion (Tenuate) and phentermine (Adipex) are approved by the Food and Drug Administration (FDA) for only short-term use — generally less than 12 weeks. Orlistat (Xenical), lorcaserin (Belviq) and a combination drug (Qsymia) are approved by the FDA for long-term use. Qsymia contains phentermine and an extended-release (ER) form of topiramate. Orlistat is also available in a reduced-strength form without a prescription (Alli).

The chart shows the commonly used prescription weight-loss drugs, how they work and their side effects.

Diethylpropion (Tenuate), phentermine (Adipex-P), benzphetamine (Didrex) and phendimetrazine (Bontril) are approved for only short-term use — generally less than 12 weeks. These drugs are classified as controlled substances because they have the potential to be abused. Because of possible side effects, these drugs aren't recommended if you have heart disease, high blood pressure or hyperthyroidism.

Orlistat (Xenical), lorcaserin (Belviq), phentermine-topiramate (Qsymia), naltrexone-bupropion (Contrave) and liraglutide (Saxenda) are approved for long-term use. Orlistat is also available in a reduced-strength form without a prescription (Alli). Limiting your intake of dietary fat is critical when taking orlistat.

After orlistat was approved, rare cases of serious liver injury were reported in some people taking it. No cause-and-effect relationship was established between orlistat and liver injury. However, Xenical and Alli labels now advise people taking orlistat to be alert to signs and symptoms that could indicate liver injury, such as itching, loss of appetite, yellow eyes or skin, light-colored stool, or brown urine.

Lorcaserin (Belviq) initially raised concerns because it works somewhat like fenfluramine — which was withdrawn from the market because it damaged heart valves. However, there is no evidence that Belviq damages heart valves. Belviq may increase heart rate, so people taking it may need to have their heart rate checked.

The combination drug Qsymia (phentermine and topiramate) increases the risk of birth defects. Thus, the Food and Drug Administration (FDA) required the manufacturer to have a risk evaluation and mitigation strategy (REMS). The REMS is intended to alert women to the risks and explain the need to avoid becoming pregnant while taking Qsymia. In addition, Qsymia is considered a controlled substance because one of its ingredients — phentermine — has the potential for abuse.

The combination drug Contrave contains naltrexone and bupropion. Naltrexone is used to treat alcohol and opioid dependence, while bupropion is an antidepressant that often reduces the risk of weight gain in people who are trying to quit smoking. Contrave also can raise heart rate and blood pressure and may increase the risk of seizures. Bupropion can increase the risk of suicidal thoughts and behaviors.

Liraglutide (Saxenda) is the newest drug to be approved for weight loss. The FDA approved it with the requirement that the manufacturer have a REMS to inform doctors about the serious risks associated with Saxenda. Saxenda has a boxed warning stating that tumors of the thyroid gland have been observed in animal studies but that it is unknown whether Saxenda causes these tumors in humans. Unlike the other weight-loss drugs, Saxenda is administered by injection once daily.

If you meet the criteria for prescription weight-loss drugs, you and your doctor will need to evaluate the potential benefits against the possible risks of taking the medicine. Cost also is a consideration. Not all health insurance plans cover prescription weight-loss drugs.

As you consider weight-loss drugs, make sure that you make every effort to exercise, change your eating habits and adjust any other lifestyle factors that have contributed to your excess weight.

Weight-loss drugs aren't the easy answer to weight loss, but they can be a useful tool to help you make the necessary diet and lifestyle changes. Keeping off the pounds you've lost, however, is an ongoing concern. And many people, despite their efforts, still regain the weight.

References

Prescription medications for the treatment of obesity. National Institute of Diabetes and Digestive and Kidney Diseases. http://win.niddk.nih.gov/publications/prescription.htm#meds. Accessed Jan. 23, 2015.

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